Oxidation of Ce(III) to Ce(IV) by Ozone in Nitric Acid Medium Using a Static Mixer: Mathematical Modeling and Experimental Validation

Abstract

This paper deals with a cerium based redox chemical process which is employed to remove fixed radioactive contaminants from alpha bearing metallic surfaces, worldwide. Oxidation of cerium to its fourth valence state is a crucial step of this process. We present an inactive bench scale study to obtain the effect of various process parameters on conversion of Ce­(III) to Ce­(IV) by ozone in nitric acid medium, using an SMX type of static mixer. Two different mathematical models, one considering a simple semibatch mixed reactor configuration and another based on the concept of axial dispersion, were developed for predicting Ce­(III) conversions using the said static mixer, in a full recycle mode. Simulation results from the models matched fairly well to experimental data, with respective mean absolute percentage deviations of 21.1% and 17.4%, computed over all the parameters. An attempt to extend these models for other non-nuclear environmental applications is also described.

A HNO3‐Responsive Aqueous Biphasic System for Metal Separation: Application towards CeIV Recovery

“…The process schematic is summarized in Figure 4A and constitutes five major steps: (1) leaching in 2.0 mol L −1 H 2 SO 4 , (2) recovery of REEs by double sulfate (DS) precipitation, (3) cerium oxidation using NaOH, (4) dissolution of the precipitate in HNO 3 and Ce IV recovery by AcABS, and (5) IL regeneration. The conversion of Ce III to Ce IV is accessible in acidic HNO 3 solutions using strong oxidants such as ozone (standard electrode potential of E 0 =1.743 V vs. E 0 =2.076 V), [40–42] theoretically permitting the “one‐pot” Ce IV oxidation and separation in AcABS. However, the presence of species with competing redox potentials, notably Mn II/IV ( E 0 =1.240 V) [43] meant the REEs first had to be separated from the transition metals in an additional Step (2) that also influenced the leaching acid selection.…”